#include<iostream>
#include<vector>
#include<array>
using namespace std;

int main()
{
	const int num = 4;
	vector<double>vd{ 1.2,1.3,1.4,1.5 };
	array<double, num>arr{ 1.7,1.8,1.9,2.0 };
	
	vd[-1] = 9.0;
	cout << vd.at(0) << endl;
	cout << vd.at(-1) << endl;
	cout << vd[-1] << endl;
	
	return 0;
}
